Power converter, motor driving unit, and electric power steering device

Abstract

A power converter includes a first inverter, a second inverter, and a switching circuit including first and second switching elements. In a state in which, in the first inverter, potentials at a first node in a high side and a second node in a low side are equal to each other, and potentials at first ends of two-phase windings of n-phase windings with n being an integer of 2 or more are equal to each other, two-phase windings are energized using two legs connected to second ends of the two-phase windings of n legs of the second inverter while performing switching operations on the first and second switching elements of the switching circuit at a predetermined duty ratio.

The invention claimed is: 
     
       1. A power converter to convert power from a power supply into power supplied to a motor with n-phase windings where n is an integer of 2 or more, the power converter comprising:
 a first inverter connected to a first end of each of the n-phase windings of the motor and including n legs each including a low-side switching element and a high-side switching element; 
 a second inverter connected to a second end of each of the n-phase windings and including n legs each including a low-side switching element and a high-side switching element; and 
 a switching circuit including a first switching element to switch connection and disconnection between the first inverter and a ground and a second switching element to switch connection and disconnection between the first inverter and the power supply, the first switching element and the second switching element being structured to cut off a bidirectional current; wherein 
 in a state in which, in the first inverter, potentials at a first node in a high side, to which the n legs are connected, and a second node in a low side, to which the n legs are connected, are equal to each other, and potentials at first ends of two-phase windings of the n-phase windings are equal to each other, the two-phase windings are energized using two legs connected to the second ends of the two-phase windings of the n legs of the second inverter while performing switching operations on the first and second switching elements of the switching circuit at a predetermined duty ratio. 
 
     
     
       2. The power converter of  claim 1 , wherein the switching circuit further includes a third switching element to switch connection and disconnection between the second inverter and the ground, and a fourth switching element to switch connection and disconnection between the second inverter and the power supply. 
     
     
       3. The power converter of  claim 1 , wherein n is an integer of 3 or more, and when an n−2-phase winding of the n-phase windings has failed, in a state in which, in the first inverter, potentials at the first node in the high side and the second node in the low side are equal to each other, and potentials at first ends of non-failed two-phase windings of the n-phase windings are equal to each other, the two-phase windings are energized using two legs connected to the second ends of the two-phase windings of the n legs of the second inverter while performing switching operations on the first and second switching elements at the predetermined duty ratio. 
     
     
       4. The power converter of  claim 1 , wherein when an n−2-phase winding of the n-phase windings has failed and the first inverter includes a failed switching element, in a state in which, in the first inverter, potentials at the first node in the high side and the second node in the low side are equal to each other, and potentials at first ends of non-failed two-phase windings of the n-phase windings are equal to each other, the two-phase windings are energized using two legs connected to the second ends of the two-phase windings of the n legs of the second inverter while performing switching operations on the first and second switching elements at the predetermined duty ratio. 
     
     
       5. The power converter of  claim 3 , wherein, when the non-failed two-phase windings are energized, in the first inverter, both the low-side switching element and the high-side switching element included in at least one of the n legs are in an on state. 
     
     
       6. The power converter of  claim 5 , wherein the high-side switching element included in one of the two legs connected to the first ends of the non-failed two-phase windings is in an on state, and at least one of the high-side switching element and the low-side switching element included in the other one of the two legs is in an on state. 
     
     
       7. The power converter of  claim 5 , wherein the low-side switching element included in one of the two legs connected to the first ends of the non-failed two-phase windings is in an on state, and at least one of the high-side switching element and the low-side switching element included in the other one of the two legs is in an on state. 
     
     
       8. The power converter of  claim 1 , wherein a duty ratio is 50%. 
     
     
       9. The power converter of  claim 1 , wherein the power supply includes a first power supply for the first inverter and a second power supply for the second inverter. 
     
     
       10. A motor driving unit comprising:
 the motor; 
 the power converter of  claim 1 ; and 
 a control circuit to control the power converter. 
 
     
     
       11. An electric power steering device comprising:
 an auxiliary torque mechanism; and 
 the motor driving unit of  claim 10 .